(In reply to comment #2)
> break _mesa_problem
> Function "_mesa_problem" not defined.
> Make breakpoint pending on future shared library load? (y or [n]) y
> Breakpoint 1 (_mesa_problem) pending
That's fine, the breakpoint should be resolved as soon as libGL is loaded.
> I try to play video with Mplayer only. But it's ok.
Maybe it doesn't use GL output, try running it with -vo gl or -vo gl2.
> I try to get a backtrace from Smpalyer.
> I've got previous error, then type: bt all.
The backtrace doesn't look related to the problem reported here. Maybe it's from a different thread, a different problem, or simply from a signal that gets handled by smplayer.

I don't know what is "mesa_7_4_branch".
In x11 overlay i have only this packages:
-mesa-7.5_rc2
-mesa-9999
In offical packages tree i have only this:
-....
-media-libs/mesa-7.4.1-r2
-media-libs/mesa-7.4.2
Where i can find mesa_7_4_branch?